I'm french and I need help to choose between a few English names for my mini video game. It's about a sort of angry dark Pac-Man with teeth. It crunches buildings and people (hey, it's only a game, nobody was hurt).

I provide a picture to show the context:

Here are the few names I have in mind:
1/ city cruncher
2/ cities cruncher
3/ city's cruncher
4/ cities's cruncher

When I apply Google translate on them, the 3 and 4 are better fitting my idea. But for me the "'s" seems harder to spell/read/memorize, particularly for the 4.

Your first choice is the best choice: city cruncher. As a product name, it should be capitalized as City Cruncher.

So why is this the best choice? In English, when the word “city” is used as an adjective, we usually don’t make it possessive. So, for example, we say: city slicker, city mayor, city library, city beach.

Even though your Cruncher may be crunching more than one city, he’s still a City Cruncher (not a Cities Cruncher), the same way that the Drugstore Cowboy was so-called even though he was stealing drugs from more than one drugstore. We would never call him a Drugstores Cowboy. That sounds really awful.